Fluid pressure gauge



Jan. 11, 1955 G. B. BAILEY 2,699,069

FLUID PRESSURE GAUGE Filed June 24, 1943 s Sheets-Sheet 1 INVENTOR-fizoea: 6,15A/L5Y.

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United States Patent FLUID PRESSURE GAUGE George E. Bailey, Long Beach,Ind., assignor to The Hays Corporation, Michigan City, Ind., acorporation of Indiana Application June 24, 1948, Serial No. 34,960

7 Claims. (Cl. 73398) This invention relates to improvements in fluidpressure gauges.

The primary object of the invention is to provide a fluid pressure gaugewhich employs an unbonded strain gauge as the measuring element thereof.

A further object is to provide a device of this character wherein afluid, preferably a dielectric fluid such as oil, serves as the pressuretransmitting means to prevent contact of the measuring element with anyconductor and to prevent access of condensate to the measuring element.

A further object is to provide a device of this character which is soconstructed as to avoid any error due to extraneous conditions, such asvariation in temperature or differences in the rate of effect of changesin temperature in different parts of the unit.

A further object is to provide a device of this character having ameasuring diaphragm of novel construction and novel mounting.

A further object is to provide a device of this character which may beutilized either to measure static pressure or to measure the differenceof two pressures.

Another object of the invention is to provide a device of this characterwhich is adapted to measure pressures within a wide range, for example,a range of pressures from one inch of water pounds per square inch) orfractions thereof, to pressures in the neighborhood of 125 pounds persquare inch.

Other objects will be apparent from the following specification.

In the drawing:

Fig. 1 is an end view of the device with parts broken away.

Fig. 2 is a view of the device with parts shown in section, taken online 22 of Fig. 1.

Fig. 3 is a longitudinal detail sectional view of one embodiment of themeasuring element taken on line 3-3 of Fig. 4.

Fig. 4 is a face view of the measuring element.

Fig. 5 is a view similar to Fig. 2, illustrating the application of theinvention to a differential pressure measuring device.

Referring to the drawings which illustrate the preferred embodiments ofthe invention, and particularly to Figs. 1 and 2 which illustrate theapplication of the invention to a pressure gauge, the numerals designatemounting or backing members provided with apertures 11 adapted toreceive securing means for anchoring the same to a support or a casing.The members 10 support a body or housing having a large diametercylindrical end portion 12 and a smaller portion 13 having a boreextending from end to end therethrough and preferably being of square orrectangular outer cross-sectional shape, said parts interfitting andbeing fixedly secured together, as by welding, at 14. The end of thelarge diameter portion 12 of the housing is spanned by an end plate 15held in place by securing members or screws 16. The plate 15 preferablyhas a filling opening or port 17 formed therein normally sealed by athreaded plug or needle valve 18. A gasket ring 19 is seated in amarginal recess at the mouth of the member 12 and is engaged and pressedupon by the plate 15 to form a seal at the joint between the casingparts 12 and 15.

The outer end portion of the cylindrical casing member 12 has anenlarged inner diameter providing an annular shoulder 20. A slackdiaphragm 21, which may be formed of rubber or other flexible material,seats at 2,699,069 Patented Jan. 11, 1955 its margin against theshoulder 20, and a ring 22 bears against the outer face of saiddiaphragm and is secured to the casing member 12 by the securing screws23. The diaphragm member 20 is spaced inwardly from the end plate 15 andcooperates therewith and with the large diameter bore portion at theouter end of the member 12 to define a chamber 24. The wall of thecasing member 12 has a port 25 formed therein with which a fluidpressure conduit 26 is connected, said conduit forming the source ofsupply of the fluid whose pressure is to be measured.

A thin walled metal tube 30, preferably formed of steel, fits within thebore of the part 13 and has a snug anchorage at 31 at its inner end. Thebore of the member 13 is slightly enlarged forwardly of the anchor point31 to provide a free clearance around the major portion of the tube 30at 32. The tube 30 projects beyond the inner end of the casing part 13and mounts an annular member 33 which is preferably formed of beryliumcopper or any other alloy selected, for purposes to be mentioned herein.The ring 33 is preferably shouldered at 34 for firm anchorage with theouter end of the steel tube and preferably has a frusto-conical surface35 formed concentrically therein at its outer face. A cup-shaped metaldiaphragm 36 having a substantially cylindrical marginal portion 37 ismounted by the ring 33. In the preferred form of the invention, the ring33 has an annular groove 38 formed in its outer face concentrictherewith to receive and anchor the marginal portion of the diaphragmwall 37 so that the central part 36 of the diaphragm is spaced or offsetfrom the ring 33. The diaphragm 36, 37 is preferably formed from a metalhaving a low coefiicient of expansion. The metal of which this diaphragmis formed and the 'rnetal of which the ring 33 is formed preferably havematching coefficients of expansion. A chamber 39 is formed within thecasing member 12 between the diaphragms 21 and 36. A bore 40 is formedin the member 12 to communicate with said chamber. Said bore preferablyhas a tube 41 fitting therein with its outer end projecting outwardlyfrom the casing 12. The fit of the tube 41 within the passage 40 ispreferably a shrink fit or any other fit which will insure against theleakage of fluid around the outside of the tube. The chamber 39 isfilled with liquid, such as oil, which is introduced therein through thetube 41. After the chamber 39 is completely filled with liquid, theouter projecting end 42 thereof is sealed as by crimping and solderingor by any other suitable means. The outer end portion of the passage 40is enlarged and screw-threaded at 43, and a protective cap 44 fitsaround the projecting tube portion 42 and is threaded into the boreportion 43.

The rear or outer end of the small body portion 13 is spanned by a plate50 secured thereto by securing screws 51. The portion of the member 13at the rear or outer end thereof has a bore of larger inner diameterthan the remainder of the bore of the member 13 to provide a shoulder 52against which bears the marginal portion of a slack diaphragm 53 whichmay be formed of rubber or any other material, preferably being the samematerial of which the diaphragm 21 is formed. The diaphragm 53 isclamped in place by a ring 54 secured to the casing portion 13 by thescrews 55. A passage 56 is formed in the member 13 outwardly of thediaphragm 53, said passage constituting an atmospheric opening. Theinner end of this passage is preferably reduced and screw-threaded toreceive a screw-threaded member or plug 57 adapted to seal the deviceand to exclude dirt therefrom during shipment. The plug 57 is removedwhen the device is in use.

A measuring element 60 is mounted in the space between the diaphragms 36and 53. This measuring element preferably constitutes an unbonded straingauge and may be of the construction best illustrated in Figs. 3 and 4.A cup-shaped housing 61 has a marginal outwardly projecting transverseflange 62 at its mouth. A plate 63 spans the mouth of the casing 61 andbears against the flange 62. Screws or other suitable securing members64 extend through the flange 62, the plate 63 and into the ring 33 toanchor the casing and associated parts to said ring. Any suitable typeof strain gauge, preferably of the unbonded type, may be mounted withinthe easing. For purposes of illustration I have shown a strain gauge ofthe type comprising a plate having a mounting flange 66 bentperpendicularly therefrom at one end and adapted to be anchored at 67 tothe casing as at the wall 63 thereof. The plate 65 has a central substantially rectangular opening 68 formed therein. Ears 69 or othersuitable rigid supports are carried by the plate 65 at the opposite endsof the opening 68 thereln and are here shown as being integral with saidplate and being struck perpendicularly therefrom. The ears 69 terminatein inwardly projecting portions 70. Spnng plates 71 are fixedly anchoredat the edges of the flanges 70 and extend substantially parallel to thecars 69. The opposite ends of the spring plate 71 carry a rigid plate72, preferably arranged in the same plane as the plate 65 and of a sizesmaller than the opening 68 to be free for movement Within said openingin its plane. The spring plate is secured to the flange 70 and to theends of the plate 72 in any suitable manner, as by welding, by rivets,or the like.

An elongated rigid stem 75 extending parallel to the axis of the casing12, 13 is fixedly anchored to the plate 72 at one end 76 thereof as bywelding. The stem 75 is laterally spaced from and substantially parallelto the plate 72 and extends freely through an opening 77 in one of thespring plates 71, an opening 78 in the adjacent car 69, an opening 79 inthe flange 66, and an opening 80 in the plate 63. Said openings arearranged in register and the stem 75 preferably has ample clearance ineach. The forward end of the stem 75 has fixedly mounted thereon afitting having an enlarged head 81 bearing flat against the inner faceof the diaphragm portion 36 centrally of said diaphragm. An externallyscrew-threaded shank 82 projects outwardly through an opening formedwithin the diaphragm. A nut 83 is threaded on said shank and serves tofixedly clamp the diaphragm to the shank. In other words, the centralportion of the diaphragm around the opening through which the shank 82extends is firmly gripped and clamped between the nut 83 and the fittinghead 81. Consequently, any movement of the diaphragm is transmitted tothe stem and from the stem to the plate 72 of the strain gauge.

The plate 65 of the strain gauge preferably has a pair of pins 85projecting therefrom at one end and fixedly anchored to the plate 65.The pins 85 are preferably arranged symmetrically relative to thelongitudinal axis of the plates 65 and 72 and the opening 68. A pair ofpins 86 are fixedly anchored to the plate 72 at the end thereof oppositethe end adjacent to the pins 85. The pins 86 are preferably inlongitudinal alignment with the pins 85, and the resistance wire 87 iswound around each of the aligned sets of pins 85, 86 under tension. Theopposite end of the plate 65 mounts a second pair of pins 88symmetrically arranged with respect to the longitudinal axis of saidplate and spaced apart a distance less than the spacing of the pins 85.In longitudinal alignment with the pins 88 is provided a pair of pins 89fixed to the plate 72 at the end thereof remote from the pins 88, and apair of resistance wires 90 are wound around each of the longitudinallyaligned sets of pins 88, 89 and placed under tension equal to thetension of the wires 87. It will be apparent that in normal conditions,where the parts are free from any diaphragmapplied stress or strain, theelectrical conductivity of the wires 87 will be the same as theelectrical conductivity of the wires 90, it being understood that thesewires will be of the same length, material, cross-sectional size, andwill otherwise have equal and matching resistance characteristics whenplaced under stress of the same value. Insulation means of any suitabletype insulates the wires 87 and 90 from the plates 65 and 72.

The casing portion 13 is provided with a plurality of passages extendingtherethrough and communicating with the space between the diaphragms 53and 36. Electrical leads 91 from the measuring element 60 will extendthrough suitable sheaths 92 mounted in the passages. A cup-shaped casing93 is fixedly mounted upon the casing part 13 rearwardly of the casingpart 12. This casing is preferably closed by a cover 94 anchored inplace by the securing members 95 and pressing against a sealing gasketring 96 which bears against the upper open cup-shaped housing 93. Withinthe cup-shaped housing 93 are mounted posts 97 which preferably supporta partition 98. Posts 99 serve to space the partition 98 from the cover94. Suitable terminals 100 mounted within the casing 93 and fixedresistors 101 are mounted upon the platform 98. Electrical leads to thevarious components of the device may extend through a tubular neck 102.

One illustrative electrical circuit of the gauge is illustrated in Fig.4. In this form it will be seen that the two resistance coils orwindings 87 are connected by a lead 105 and the two resistance windings90 are connected by a lead 106. The fixed resistors 101 are connected toprovide two legs of a Wheatstone bridge, being connected together by alead 107. The input leads 108 to the bridge are respectively connectedto a lead 109 which connects one end of one of the fixed resistors 101with one of the resistors 87 of the strain gauge and to a lead 110 whichconnects an end of the opposite fixed resistor 101 with one of thestrain gauge resistors 90. A lead 111 connects the strain gaugeresistors 87 and 90, and a lead 112 is tapped from the lead 111 andconstitutes an output lead leading to a current measuring instrument. Asecond output lead 113 is connected with the lead 107 and also isadapted to extend to the current measuring instrument. The electricalconnections are such that each of the similar resistances of the straingauge are connected electrically so that the two resistance elements 87constitute one leg of a Wheatstone bridge, and the two resistances 90constitute another leg of the Wheatstone bridge. The input and outputleads to the Wheatstone bridge are so arranged that if any difference inthe electrical resistances of the resistance elements 87 and 90 occursin the circuit, the Wheatstone bridge will be unbalanced and the currentmeasuring instrument connected with the leads 112 and 113 will measureand indicate the amount of unbalance, which can be calibrated in termsof the pressure applied. The output measuring instrument (not shown) mayconstitute either an indicator or a recorder.

In the operation of the device, fluid, such as a liquid or gas underpressure, which is subject to measurement, is transmitted from theconduit 26 through the passage 25 into the chamber 24 where it actsagainst the flexible diaphragm 21. The chamber 39 which is filled withliquid is subjected to the pressure in the chamber 24, and the oil orother liquid in the chamber 39 form means for transmitting the pressurein the chamber 24 to the measuring diaphragm 36. The diaphragm 36, beingformed from metal and preferably configured substantially as shown sothat it does not constitute a flat member, but instead has an offset endwall which is provided with circular concentric bends, is sufiicientlyflexible to trans mit the pressure to and through the stem 75 to actuatethe strain gauge 60. As the stem 75 is urged longitudinally, itincreases the tension of one set of resistors, here shown as resistors90, and releases the tension upon the resistors 87. This varies theresistance values of said resistors and unbalances the bridge so thatthe bridge output may be read as a measure of gas pressure. Observe thatthe chamber in which the strain gauge element is located is filled witha non-conductive liquid, such as oil, and that this oil is free to enterthe space behind or within the diaphragm 36. Inasmuch as the range ofmovement of the diaphragm is limited, no problem of oil displacement isencountered. In actual practice the full range of movement of thediaphragm is in the order of .001 inch. This movement is obviously sosmall as not to produce any substantial liquid displacement effect orproblem, and any displacement which occurs is accommodated by theflexible diaphragm 53. In the preferred form of the device, the oil isretained within the rear or inner portion of the part 13 to immerse thestrain gauge 60 and is prevented from entering the chamber 93. In thisconnection the tubes 92, which pass through the casing openings and leadthe terminals or leads 91 into the chamber 93, are preferably projectedinto the housing 93 and crimped or otherwise sealed at 93, as bestillustrated in Fig. l. The immersion of the strain gauge in the oilinsulates said gauge from condensate or other conductive moisture.

The shape of the diaphragm forms one of the important features of thisinvention. Observe that the cup-shaped form provides the cylindricalwall portion 37 to offset the transverse pressure measuring surface ofthe diaphragm from its mounting ring 33. The importance of thisconstruction is that it provides means for avoiding any error inmeasurement due to temperature effects, that is, from effects due to anydifference in the rate of response to changes of temperature upon thediaphragm 36, 37 and upon the ring 33. The mass of the ring 33 is muchgreater than the mass of the diaphragm, and this difference in mass,even in cases where the coeificient of expansion of the materials ofwhich the diaphragm and its mounting are formed are substantially equal,will tend to produce a difference in the rate of response of these partsto changes of temperature. Any difference occurring in this respect, dueto temperature efiects, can be absorbed by the cylindrical marginalportion 37 of the diaphragm. Thus a tendency of the ring 33 to expandradially or circumferentially compared to the diaphragm is absorbed andtaken up by the cylindrical diaphragm portion 37 which is free to flexradially without flexing the transverse end or working portion 36 of thediaphragm. It will be obvious that the construction herein illustrated,wherein the sleeve 30 has clearance within its socket 32 and the ringitself has clearance from both the end and the circumferential walls ofthe chamber of the housing 12 in which it is received, permit the freeresponse of the ring 33 to temperature effects without injury thereof orinterference with the other working parts of the device. It may bementioned that the effect of the difference of the rate of temperatureresponse is minute and under ordinary conditions in measuring deviceswould not be critical. However, where, as mentioned before, a straingauge is used as the measuring element and its full range of movement isin the neighborhood of only .001 inches, the small or minute temperatureeffect becomes critical. Thus where the difference in temperatureeffects between the ring and its mounting would be as low as .000001inch, the same would be measurable by the instrument and would detractfrom its accuracy if the diaphragm unit were not constructed in a mannerto compensate for the effect. It might be mentioned in this connectionthat the mounting of a flat or substantially unskirted diaphragm withina mounting ring of greater mass would cause, when subjected to the sametemperature effects mentioned, a distortion or buckling of the diaphragmwhich would introduce an appreciable error in the readings obtained, dueto the actuation of the strain gauge by this distorting or bucklingaction.

The application of the invention to a device intended to measuredifierential pressure, such as a flow meter, is illustrated in Fig. 5.This device entails substantially the same construction and arrangementof parts hereinabove mentioned, and, to the extent that the partsthereof are similar to the parts in the device illustrated in Figs. 1 to4, said parts bear the same reference numerals. In order to apply thepressure differential to the measuring device, an elongated block 120 issecured fixedly to the large diameter portion 12 of the casing andprojects rearwardly and below the small portion 13 of the casing. Thecasing has a pair of bores extending therethrough, one of which bores isjoined with the passage 25 as by means of a sleeve 121. A fluid line 122is connected with this bore, and a valve 123, such as a needle Valve, ismounted in the block to control the flow of fluid from the conduit 122through the connected bore of the block, the sleeve 121 and the passage25 to the chamber 24. The second bore is connected with the passage 56in the part 13 of the device by means of a tube 124. An inlet conduit125 is connected with this bore, and the valve 126 is provided tocontrol the flow of fluid from the conduit 125 through the communicatingbore, the tube 124 and the passage 56. Further, to accommodate theapplication of the device for use as a differential pressure gauge, therear plate 50 of the gauge is provided with a passage 127 which mounts aplug or needle valve 128.

In view of the fact that the space in the device between the diaphragms21 and 53 is filled with liquid, the pressure applied at the chamber 24is transmitted by the liquid in the chamber 39 to one surface of thediaphragm 36, and the pressure applied through the inlet 125 to actagainst the diaphragm 53 is transmitted to the liquid between thatdiaphragm 53 and the diaphragm 36 in a direction opposite to thedirection of application of the first mentioned pressure. For thispurpose suitable openings (not shown) will be provided either in thehousing 60 of the strain gauge or in the diaphragm mounting ring 33, sothat no barrier exists to interfere with the flow of liquid to transmitthe pressure applied at the diaphragm 53 to the diaphragm 36. Thisdevice possesses all of the other advantages hereinabove referred towith reference to the construction illustrated in Figs. 1 to 4.

The problem of compensation for errors arising as the result of changesin temperature are common to both forms of the device illustratedherein. The arrangement of the parts, and particularly the skirtedcharacter of the diaphragm 36, the liquid immersion of the strain gauge60, and the location of the resistors 101 externally of the liquidchamber, serves to hold temperature errors to a minimum. Furthercompensation for any temperature errors which may occur can be providedby including, as a part of each of the fixed resistors 101, atemperature sensitive compensating resistor element. In this way anelectrical temperature compensation, in addition to the mechanicaltemperature compensation mentioned above, is provided in the device. Itmight be mentioned in this connection that the use of such temperaturesensitive compensating resistor elements is made possible by thelocation of those elements externally of the oil-filled chamber withinwhich the strain gauge or other transmitter 60 is located. If the entireWheatstone bridge circuit were encased in the oil-filled chamber, theaddition and adjustment of such temperature sensitive resistors to thecircuit would present serious problems and would be impractical. The useof such temperature sensitive resistor elements outside of theoil-filled chamber is practical and feasible, however, and produces anincreased accuracy of response of the gauge to the fluid condition beingmeasured.

While the preferred embodiments of the invention have been illustratedand described herein, it will be understood that changes in theconstruction may be made within the scope of the appended claims withoutdeparting from the spirit of the invention.

1 claim:

1. A pressure gauge comprising a housing, a pressure responsive unitmounted in said housing and including a diaphragm and an electricaltransmitter actuable by said diaphragm, a second diaphragm spanning saidhousmg spaced from said first diaphragm and cooperating therewith todefine a sealed chamber in said housing, sa d housing having a fluidinlet chamber separated from said sealed chamber by said seconddiaphragm, a fluid lme communicating with said inlet chamber, a liquidfilling said sealed chamber and serving to transmit to said firstdiaphragm the pressure applied by the fluid in said inlet chamberagainst the second diaphragm, a metal r ng, said first diaphragm beingmounted on said metal ring, said first diaphragm being formed of metalhavingsubstantially the same temperature coefficient of expansion as themetal of said ring, and means mounting said ung in said housing withclearance for thermal expansron therein.

2. A pressure gauge comprising a housing, a pressure responsive unitmounted in said housing and including a diaphragm and an electricaltransmitter actuable by said diaphragm, a second diaphragm spanning saidhousmg spaced from said first diaphragm and cooperating therewith todefine a sealed chamber in said housing, said housing having a fluidinlet chamber defined in part by said second diaphragm, a fluid linecommunicating with said inlet chamber, a liquid filling said sealedchamber and serving to transmit to said first diaphragm thepressureapplied by the fluid in said inlet chamber against the second diaphragm,said first diaphragm constituting a cup-shaped metal member having abent end wall and a cylindrical skirt, means connecting said transmitterwith the end wall of said diaphragm, and elongated tubular mountingmeans carried by said housing at one end and circumferentiallysupporting the margin of the skirt of said diaphragm at its oppositeend.

3. In a fluid pressure gauge, a housing having a chamber, a fluid inletcommunicating with said chamber, a metal diaphragm, a rigid annulusmounting said diaphragm, metal tube mounting said annulus andcontinuously circumferentially secured to said housing, a seconddiaphragm spanning said chamber between said inlet and said firstdiaphragm, an electrical transmitter, said first diaphragm having an endportion with concentric bends and a marginal skirt projecting laterallyfrom said end portion and anchored to said annulus, and a connectorsecured to the end portion of said first diaphragm and actuating saidtransmitter in response to variation in the position of the end portionof said first diaphragm.

4. In a fluid pressure gauge, a housing having a chamber, a fluid inletcommunicating with said chamber, a metal diaphragm, a rigid annulusmounting said diaphragm, a support mounting said annulus and carried bysaid housing, said diaphragm, annulus and support cooperating to form asealed partition in said housing, a second diaphragm spanning saidhousing between said first diaphragm and said inlet, an electricaltransmitter, said first diaphragm having an end configured portion and amarginal skirt projecting laterally from said end portion and anchoredto said annulus, and a connector secured to the end portion of saidfirst diaphragm and actuating said transmitter in response to variationin the position of the end portion of said first diaphragm, said annulusbeing formed of metal having substantially the same coefficient ofexpansion as said first diaphragm.

5. In a fluid pressure gauge, a housing having a chamber, a fluid inletcommunicating with said chamber, a metal diaphragm, an annulus mountingsaid diaphragm and sealingly secured to said housing, a second diaphragmspanning said housing between said first diaphragm and said inlet, anelectrical transmitter, said first diaphragm having an end portion and amarginal skirt projecting laterally from said end portion and anchoredto said annulus, and a connector secured to the end portion of saidfirst diaphragm and actuating said transmitter in response to variationin the position of the end portion of said first diaphragm, said annulusbeing of smaller cross-sectional size than said chamber and positionedin said housing with clearance therearound, and a tube anchored at oneend to said housing and mounting said annulus at its opposite end.

6. In a fluid pressure gauge, a housing having a chamber, a fiuid inletcommunicating with said chamber, a metal diaphragm, an annulus mountingsaid diaphragm, a member mounting said annulus and carried by saidhousing to define a sealed partition in cooperation with said annulusand diaphragm, an electrical transmitter, said diaphragm having anundulating end portion and a marginal skirt projecting laterally fromsaid end portion and anchored to said annulus, and a connector securedto the end portion of said diaphragm and actuating said transmitter inresponse to variation in the position of the end portion of saiddiaphragm, a second diaphragm spanning said housing between said firstdiaphragm and said inlet, said transmitter comprising an electricalstrain gauge having a pair of resistors, said resistors being arrangedwhereby one thereof is stressed upon movement of said first diaphragm inone direction and the other is stressed upon movement of said firstdiaphragm in the opposite direction.

7. In a fluid pressure gauge, a housing having a chamber, a fluid inletcommunicating with said chamber, a metal diaphragm, a rigid annulusmounting said diaphragm, a member mounting said annulus and carried bysaid housing to sealingly space said chamber in cooperation with saidannulus and diaphragm, an electrical transmitter, said diaphragm havingan end configured portion and a marginal skirt projecting laterally fromsaid end portion and anchored to said annulus, a connector secured tothe end portion of said diaphragm and actuating said transmitter inresponse to variation in the position of the end portion of saiddiaphragm, said transmitter including two variable resistors, a seconddiaphragm spanning said chamber between said inlet and first chamber,and an electrical circuit including two fixed resistors connected tosaid variable resistors to form a Wheatstone bridge.

References Cited in the file of this patent UNITED STATES PATENTS2,059,549 Carlson Nov. 3, 1936 2,220,902 Hastings et al. Nov. 12, 19402,276,580 Hofer Mar. 17, 1942 2,421,907 Postlewaite June 10, 19472,435,716 Kearney Feb. 10, 1948 2,459,268 Elkins Jan. 18, 1949 2,466,071Barnes et al. Apr. 5, 1949 2,466,846 Giesler Apr. 12, 1949 2,539,892Cook Jan. 30, 1951 2,664,749 Jones Jan. 5, 1954

